The class of linear alternating polymers of carbon monoxide and at least one ethylenically unsaturated hydrocarbon has been known for some time. Nozaki, U.S. Pat. No. 3,694,412, produced such polymers in the presence of arylphosphine complexes of palladium moieties and certain inert solvents. More recent methods for the production of such polymers, now known as polyketones or polyketone polymers, are illustrated by a number of published European Patent Applications including Nos. 121,965, 181,014, 213,671 and 257,663. These processes involve the use of a catalyst composition employed in a reaction diluent. The catalyst composition typically comprises a compound of palladium, cobalt or nickel, the anion of a strong non-hydrohalogenic acid and a bidentate ligand of phosphorus, arsenic, antimony or nitrogen.
The polymerization process is usefully conducted by a variety of procedures. In a batchwise process, the reactants, catalyst composition and the reaction diluent are charged to a suitable reactor. As the polymerization proceeds, the pressure decreases, the concentration of polymer suspended in the reaction diluent increases and the viscosity of the product mixture increases until further polymerization would pose a significant problem of heat removal. At or before this point the polymerization is terminated. In this modification of the process, only the reaction temperature has remained constant. In a variation of the process, polymerization is conducted through continuous provision of additional reactants so that the pressure as well as the temperature remains constant.
Better results are often obtained through the use of a continuous process in which the reactant monomers, the reaction diluent and the catalyst composition are continuously added to the reactor and polymer suspension is continuously withdrawn from the reactor. In this procedure the reaction pressure and temperature as well as the liquid volume within the reactor remain constant. After an "initiation" or "start-up" period in which the polymer suspension increases, the reaction reaches a steady state in which the polymer suspension removed from the reactor is of a substantially constant composition and the polymer product has substantially constant properties.
In such a continuous polymerization process, one important property of the polymeric product is bulk density. In general, the higher the bulk density of the polymer product, the greater the amount of polymer that can be produced in a reactor of given volume. In addition, the volume of liquid required for washing or purifying the polymer will be lower per unit weight of polymer when polymers of relatively high bulk density are produced. It is also desirable to conduct the polymerization so that a high polymer suspension concentration will be obtained in order to minimize the volume of liquid processed during the polymerization.
The polymer suspension concentration and the bulk density of the polymer product are to some degree influenced by any initiation or start-up procedure employed in the polymerization process. If this start-up procedure can be controlled, desirable polymer suspension concentrations and polymer bulk densities are obtained when the polymerization has reached a steady state. It would therefore be of advantage to provide an improved start-up procedure for polymerization of carbon monoxide and at least one ethylenically unsaturated hydrocarbon to produce linear alternating polymers.